Post-natal neovascularization programs are engaged in pathophysiologic states ranging from tumorigenesis to chronic inflammatory disease. The generation of pro-angiogenic growth factors induces endothelial cells to penetrate the underlying basement membrane, infiltrate the surrounding interstitial tissues and re-assemble to form patent tubules. Paralleling these events, endothelial precursor cells are mobilized and collaborate in neovessel formation by recapitulating vasculogenic programs similar to those activated during development. In both cases, increasing evidence supports a model wherein a family of membrane-anchored matrix metalloproteinases, termed the MT-MMPs, plays a dominant role in endothelial cell invasion programs as well as tubulogenesis. Nevertheless, the molecular events that regulate MT-MMP-dependent proteolysis in vivo remain both undefined and controversial. In considering potential "master switches" capable of orchestrating pro-angiogenic activity, an analogy might be drawn to the epithelial-mesenchymal cell transition (EMT) programs that control branching morphogenesis in epithelial cells. Like endothelial cells, epithelial cells likewise overlay an intact basement membrane, and can be stimulated to disassemble cell-cell and cell- matrix adhesive interactions, adopt an invasive phenotype and invade surrounding structures to re-form tubulogenic networks. In this latter scenario, the zinc-finger transcriptional repressor, Snail1, has been shown to play a required role in developmental EMT with knockout mice displaying an early embryonic lethal phenotype. As neovascularization bears similarities to classic EMT programs, and Snail1 has recently been shown to regulate MT-MMP-dependent proteolysis, a series of in vitro, ex vivo and in vivo preliminary studies were launched as a means to test the hypothesis that Snail1 serves as a critical regulator of vasculogenesis and angiogenesis. To this end, we have generated a unique cohort of endothelial cell-specific Snail1-, MT1-MMP- and MT2-MMP-knockout mice as well as MT1-MMP BAC transgenic rescue mice that allow for the testing of a new series of hypotheses that Snail1 serves as a novel inducer of vasculogenesis/angiogenesis by controlling the 3-dimensional mobilization of MT- MMP to invadopodia-like structures via exocyst trafficking. As such, the following three aims are proposed: i) identify Snail1 as a key regulator of postnatal neovascularization, ii) characterize the function and regulation of the Snail1-MT-MMP-exocyst invadopodia axis during endothelial cell invasion and morphogenesis, and iii) define the endothelial cell-specific role of MT1-MMP/MT2-MMP during neovascularization ex vivo and in vivo. PUBLIC HEALTH RELEVANCE: Angiogenesis, or the development of new blood vessels, plays critical roles in health and disease. For example, in the absence of angiogenesis, wounds cannot heal while the pathologic activation of angiogenesis promotes cancer cell growth and metastasis. The outlined project uses sophisticated molecular biology techniques, cutting-edge imaging tools and novel mouse (transgenic/knockout) models to identify the key molecules that regulate blood vessel formation. The characterization of the pro- and anti-angiogenic molecules that control blood vessel formation will have important implications for the development of new therapeutic interventions.